1. Field of Invention
The present invention relates to measuring methods and apparatuses and, more particularly, is directed towards methods and apparatuses for measuring minute quantities of antigens, antibodies, and other substances.
2. Description of the Prior Art
Methods for detecting and measuring antigens and antibodies are based on the very specific reactions between an antigen and its specific antibody. Often these reactions produce effects, like precipitation or agglutination, which are visible to the naked eye. Very often, however, a clinically significant concentration of the antigen (or antibody) is so small that visual methods are not applicable and sensitive instrumentation and methods are required for its determination. Presently, the most sensitive method is radioimmunoassay (RIA), which makes use of a specific antibody (or antigen) tagged with a radioactive tracer, whose concentration at the final stage of the appropriate procedure gives the concentration of the antigen (or antibody) originally present in the sample.
The radioactive tracer is typically Iodine 125, a gamma emitting isotope of Iodine. The gamma counters used for measuring the tagged reagent can detect down to about 10.sup.-10 g. of the antigen (or antibody), or typically .gtoreq.10.sup.9 antigen particles (or antibody molecules).
Two serious problems with RIA are long incubation times and the use of radioactive tagging agents with short half-lives. Long incubation times may lead to sample deterioration caused, for example, by the action of proteolytic enzymes present in human plasma. Radioactive tagging agents with short half-lives become unusable in a relatively short time, which increases the cost of the assays.